Research on measurement and source distribution of atmospheric NO2 concentration by ground-based MAX-DOAS system in Nanjing, China

Nanjing, as one of the important cities in the Yangtze River Delta of China, has a developed economy and a large population. Although the concentration of air pollutants in Nanjing has declined with the introduction of China’s strict air pollution prevention and control policies, the situation of air pollution is still severe. Therefore, understanding the source and distribution of atmospheric pollutants has an important role in implementing the prevention and controlling of atmospheric pollutants. In this study, we observed the vertical distribution characteristics of tropospheric NO₂ by used the ground-based Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique in Nanjing. The contribution of transregional transport to NO₂ in different seasons and different altitudes (200m, 500m, and 1000m) was analyzed by combining the potential source distribution model (PSCF). The analysis results showed that the distribution of NO₂ sources were obvious seasonal changes. Due to the lower wind speed in spring, the distribution of NO₂ sources at all altitudes was not obvious. In summer and autumn, the source of NO₂ in the lower altitudes (200m) was concentrated in the urban area of ​​Nanjing and central Jiangsu Province. But for the winter, the NO₂ concentrations of lower altitudes were seriously affected by Chuzhou and Ma'anshan area. The sources distribution in the middle and upper altitude were relatively scattered and the WPSCF value was smaller than lower altitudes, which may be caused by the NO₂ concentrated in the near ground.